Diagnosis & Treatment of Phenylketonuria (PKU)

    Phenylketonuria is an inborn error of metabolism characterized by high levels of the amino acid phenylalanine [Phe] in the blood of newborns. PKU is diagnosed by means of the Guthrie Test., devised by Dr Robert Guthrie (1916 - 1995) after the birth of his own child with PKU. A small drop of blood is taken from the heel of a newborn (left) and applied to a card [right]. In the original form of the test, a punch-out of the dried disc was incubated on a petri dish plated with bacteria (Bacillus subtilis) in the presence of a growth inhibitor, B-2-thienyl-alanine. High levels of Phe in the blood sample overcome the inhibition, and allow the bacteria to grow. If an elevated level of Phe is detected, the child is placed on a phenylalanine-restricted diet for the first several years (< 10 years). This can completely offset the expected neurological effects (below). The Guthrie test was the first widely-used perinatal biochemical test, and since its introduction in the early 1960s has been used in >90% of North American hospitals.

    The original test has been supplanted by direct
mass-spectroscopy measurement of Phe concentration. Children in families at risk for PKU may also be screened by prenatal PCR-based DNA tests for the PKU-related alleles themselves.

    Recent evidence suggests that high levels of [Phe] may impair mental performance later in life, and that a Phe-restricted diet should be maintained throughout life.

    See [http://www.nspku.org/] and [http://www.macpad.org/] for more details from PKU support groups.


All text material © 2014 by Steven M. Carr